Prostate cancer is the second leading cause of cancer death among males in the United States. In 1998, an estimated 185,000 men were diagnosed with prostate cancer, and more than 39,000 men died of the disease. See, S. H. Landis et al., Cancer Statistics, CA Cancer J. Clin., 48, 6 (1998). Although survival rates are good for prostate cancer that is diagnosed early, the treatments for advanced disease are limited to hormone ablation techniques and palliative care. Hormone ablation techniques (orchiectomy and anti-androgen treatments) generally allow only temporary remission of the disease. It usually recurs within 1–3 years of treatment, with the recurrent tumors no longer requiring androgens for growth and survival. D. G. Tang et al., Prostate, 32, 284 (1997). Therapy with conventional chemotherapeutic agents, such as progesterone, estramustine and vinblastine, has also not been demonstrated to be effective to halt progression of the disease.
The number of nonsteroidal anti-inflammatory drugs (NSAIDs) has increased to the point where they warrant separate classification. In addition to aspirin, the NSAIDs available in the U.S. include meclofenamate sodium, oxyphenbutazone, phenylbutazone, indomethacin, piroxicam, sulindac and tolmetin for the treatment of arthritis; mefenamic acid and zomepirac for analgesia; and ibuprofen, fenoprofen and naproxen for both analgesia and arthritis. Ibuprofen, mefenamic acid and naproxen are used also for the management of dysmenorrhea.
The clinical usefulness of NSAIDs is restricted by a number of adverse effects. Phenylbutazone has been implicated in hepatic necrosis and granulomatous hepatitis; and sulindac, indomethacin, ibuprofen and naproxen with hepatitis and cholestatic hepatitis. Transient increases in serum aminotransferases, especially alanine aminotransferase, have been reported. All of these drugs, including aspirin, inhibit cyclooxygenase, that in turn inhibits synthesis of prostaglandins, which help regulate glomerular filtration and renal sodium and water excretion. Thus, the NSAIDs can cause fluid retention and decrease sodium excretion, followed by hyperkalemia, oliguria and anuria. Moreover, all of these drugs can cause peptic ulceration. See, Remington's Pharmaceutical Sciences, Mack Pub. Co., Easton, Pa. (18th ed., 1990) at pages 1115–1122.
There is a large amount of literature on the effect of NSAIDs on cancer, particularly colon cancer. For example, see H. A. Weiss et al., Scand J. Gastroent., 31, 137 (1996) (suppl. 220) and Shiff et al., Exp. Cell Res., 222, 179 (1996). More recently, B. Bellosillo et al., Blood, 92, 1406 (1998) reported that aspirin and salicylate reduced the viability of B-cell CLL cells in vitro, but that indomethacin, ketoralac and NS-398, did not.
C. P. Duffy et al., Eur. J. Cancer, 34, 1250 (1998), reported that the cytotoxicity of certain chemotherapeutic drugs was enhanced when they were combined with certain non-steroidal anti-inflammatory agents. The effects observed against human lung cancer cells and human leukemia cells were highly specific and not predictable; i.e., some combinations of NSAID and agent were effective and some were not. The only conclusion drawn was that the effect was not due to the cyclooxygenase inhibitory activity of the NSAID.
The Duffy group filed a PCT application (WO98/18490) on Oct. 24, 1997, directed to a combination of a “substrate for MRP”, which can be an anti-cancer drug, and a NSAID that increases the potency of the anti-cancer drug. NSAIDs recited by the claims are acemetacin, indomethacin, sulindac, sulindac sulfide, sulindac sulfone, tolmetin and zomepirac. Naproxen and piroxicam were reported to be inactive.
Recently, W. J. Wechter et al., Cancer Res., 60, 2203 (2000) reported that the NSAID, R-flurbiprofen, inhibited progression of prostate cancer in the TRAMP mouse, a prostate cancer model. The Wechter group filed a PCT application (WO98/09603) on Sep. 8, 1997, disclosing that prostate cancer can be treated with R-NSAIDs, including R(−)-etodolac and R-flurbiprofen. In contrast to R(−)-etodolac, the R-enantiomer of flurbiprofen and other (R)-2-aryl propionate NSAIDs are converted in the body to the anti-inflammatory S-enantiomers, and hence are pro-drugs of the NSAIDs, while R(−)-etodolac is not per se an NSAID. Therefore, a continuing need exists for effective methods to employ these preliminary findings to develop new compounds to treat neoplastic disease, including prostate cancer and other cancers.